Route searching device

ABSTRACT

A processor calculates an estimated travel time required to travel from a current point to a destination or a passing point on a route on the basis of a travel time represented by traffic-jam information for a traffic-jam place which is represented by the traffic-jam information received by a traffic information receiver, and on the basis of a traffic-jam time calculated on the basis of map data for the other places; accordingly, the travel time required can be calculated in consideration of traffic-jam conditions.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a technique for searching arecommendable route to a destination and calculating an estimated traveltime needed for the route in a navigation apparatus installed in avehicle, etc.

[0003] 2. Description of Related Art

[0004] With respect to a navigation apparatus installed in a vehicle,there has been known a technique of searching a route extending from adeparture place to a destination on the basis of road map data andsuggesting the route thus searched as a recommendable route to a user.

[0005] Such a recommendable route searching operation is carried out bysearching (selecting) a route needing the minimum cost in availableroutes between the departure place and the destination according to atechnique called as “Dijkstra algorithm” or the like. In this method,the total distance of the route or the travel time needed for the routeis usually selected as the “cost” defined in this method.

[0006] The estimated travel time needed for the route (hereinaftermerely referred to as “estimated travel time”) is calculated as follows.When a recommendable route is determined, the length of each of theroads constituting the recommendable route is weighted with the valuecorresponding to the type of each road (expressway, public road or thelike) to set the value thus weighted as a travel time for each road, andthe estimated travel time is calculated on the travel times for theroads.

[0007] Recently, there has been put into practice a traffic informationcommunicating system for supplying traffic information to users ofvehicles through communications, which is known as VICS (the trademarkof the foundation of Traffic Information Communication System Center).

[0008] According to this traffic information communication system,traffic information such as traffic jams, traffic regulations, etc. istransmitted from the center to vehicles by optical beacons or electricwave beacons disposed on roads or by FM multi-broadcasting, therebyenabling real-time use of traffic information in the vehicles. In aconventional navigation apparatus, when traffic regulation informationis received from such a traffic information communication system, thecontents representing the traffic regulation information are notified tousers in the form of characters, voices and displays of figures on aroad map.

SUMMARY OF THE INVENTION

[0009] The above-described conventional technique for calculating anestimated travel time needed for a recommendable route has the followingproblem.

[0010] That is, the travel time needed for the recommendable route iscalculated on the basis of fixed parameters such as the length of eachroad, the type of each road, etc., and thus when some roads of therecommendable route suffer from traffic jam for traffic regulation suchas one-way traffic or the like, the estimated travel time thuscalculated differs greatly from actual travel time.

[0011] Therefore, an object of the present invention is to calculate anestimated travel time for a recommendable route, which more meets anactual traffic condition.

[0012] In order to attain the above object, a route searching apparatusfor searching a recommendable route to a destination includes: means forstoring map data representing road maps; means for receiving traffic jaminformation representing traffic jam places and a travel time needed topass through a section in which each of the traffic jam places islocated by communication; and travel time calculating means for settingthe travel time represented by the traffic jam information as aneffective travel time for the traffic jam section represented by thetraffic jam information thus received while setting a travel timecalculated on the basis of the map data as an effective travel time forthe other sections, calculating the sum of effective travel times forrespective sections located between the current position on the searchedrecommendable road and a destination or a point on the recommendableroute for which an estimated travel time is calculated, and displayingthe sum of the effective travel times thus calculated as the travel timeneeded to travel from the current position to the destination or thepoint on the recommendable road for which the estimated travel time iscalculated.

[0013] According to the above route searching apparatus, traffic jaminformation is picked up from a traffic information communication systemsuch as VICS or the like and the estimated travel time is calculated inconsideration of the traffic jam information. Therefore, even when atraffic jam occurs or traffic regulation is carried out, an estimatedtravel time conforming to the actual traffic conditions can becalculated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a block diagram showing the constitution of a navigationapparatus according to an embodiment of the present invention;

[0015]FIG. 2 is a diagram showing the constitution of map data accordingto the embodiment of the present invention;

[0016]FIG. 3 is a flowchart showing the operation of the navigationapparatus according to the embodiment of the present invention;

[0017]FIG. 4 is a diagram showing how a dynamic travel time iscalculated according to the embodiment of the present invention; and

[0018]FIG. 5 is a diagram showing an example of a display according tothe embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] A preferred embodiment of a route searching apparatus accordingto the present invention will be described using a case where thepresent invention is applied to a vehicle-mount type navigationapparatus.

[0020]FIG. 1 shows the construction of a navigation apparatus accordingto an embodiment of the present invention.

[0021] In FIG. 1, reference numeral 1 represents a processor comprisinga microprocessor and a memory, reference numeral 2 represents a displaydevice, reference numeral 3 represents a drive device for accessing astorage medium such as CD-ROM or the like in which map data are stored,reference numeral 4 represents an input device for accepting aninstruction input of a user, reference numeral 5 represents a sensordevice comprising a vehicle-speed sensor, an azimuth sensor, a GPSreceiver, etc., and reference numeral 6 represents a traffic informationreceiving device for receiving traffic information from a trafficinformation communication system such as VICS or the like as describedabove.

[0022] Here, map data is recorded in a storage medium such as CD-ROM orthe like to be loaded in the drive device 3 will be described.

[0023] As shown in FIG. 2, the map data comprises road data 21 providedfor each road, and the road data 21 comprises road information 22 andlink information 23.

[0024] The road information 22 contains a road number 26 representing aroad uniquely, a road name 24 representing the name of a road, a roadtype 27 representing the type of road (toll road, national highway,prefectural highway), and other attributes 25 representing otherinformation for the road.

[0025] The link information 23 contains link data 28 representinginformation of links provided for every link constituting a road. Here,“link” is a line segment used for approximating the shape and positionof a road. The link data 28 contains a link number 29 representing alink uniquely and a time required 30 corresponding to a valueproportional to the length of the link.

[0026] Further, the link data 28 contains node information 31 which isinformation of a link to be next described, for example, informationrepresenting that the node is an interchange or service area of anexpressway, an intersection or the like.

[0027] Further, the link data 28 contains, for two nodes at both sidesof a link, a node number 32 representing a node uniquely, a nodecoordinate 35 representing the position of the node, and an adjacentnode number list 34 in which the node numbers of all the nodes linked tothe node concerned through links are listed. Here, the linkage betweenlinks is necessarily performed through a node. At a crossroads, a nodeis located at the center of the crossroads, and four links are linked tothe node at the center. In this case, the adjacent node number list 34of the node at the center contains the description of the node numbersof four nodes at the other ends of the four links which are linked tothe node concerned.

[0028] The link data 28 contains link shape information 36 specifyingthe shape of a link. The link shape information 36 comprises one orplural sub node coordinates 37. When the number of the sub nodecoordinates 37 is equal to two, the shape of the link is specified as ashape obtained by successively and linearly connecting a first nodecoordinate of the link, a first sub node coordinate, a second sub nodecoordinate and a second node coordinate of the link in this order.

[0029] With the above constitution, the processor 1 calculates thecurrent position of the vehicle by referring to a vehicle travel azimuthinput from the azimuth sensor of the sensor device 5, a vehicle speedinput from the vehicle-speed sensor of the sensor device 5 and mesh mapdata to which the measured current position input from the GPS receiverof the sensor device 5 belongs, and calculates an estimated route fromthe current position to the destination on the basis of a destinationinput through the input device 4 by a user and the current positioninput through the input device 4 by the user or calculated from theinput from the sensor device 5.

[0030] The processor 1 controls the drive device 3 to read out the mapdata on the basis of the current position thus calculated, the travelazimuth of the vehicle and the content indicated through the inputdevice 5 by the user, and displays a map represented by the map data onthe display device 2. The map display is carried out by displaying a mapof an area around the calculated current position on a predeterminedreduced scale, displaying a map of a district indicated by the user on apredetermined or indicated reduced scale, or displaying a map covering aregion from the current position to the destination in a proper reducedscale together with a searched recommendable route. At this time, marksrepresenting the current position and the travel azimuth of the vehicleare displayed on the map while overlaid on the map.

[0031] The estimated travel time calculation processing executed by theprocessor 1 will be described below.

[0032]FIG. 3 is a flowchart showing the estimated travel timecalculation processing.

[0033] In this processing, the link data 28 of links on a searchedrecommendable route are checked to select calculation points used tocalculate the estimated travel time. As the calculation points, thereare selected the destination, and nodes which are described in nodeinformation 31 as intersections, interchanges and service areas, orwhich serve as transfer points between different roads on therecommendable route, among nodes located in a predetermined range fromthe current position to a position on moving direction (step 301).

[0034] Next, the estimated travel time required to travel to eachcalculation point is calculated (step 302).

[0035] The calculation of the estimated travel time required isperformed as follows.

[0036] That is, for each link on the recommendable road between thecurrent position and the destination, the travel time 30 of the linkdata of each link is weighted with a value corresponding to the roadtype 27 of the road information of the road data 21 to which the linkdata 28 concerned belongs, thereby obtaining the static travel timerequired. At the same time, the link length of each link is calculatedon the basis of the link data 28.

[0037] Subsequently, a travel time required to travel between atraffic-jam starting point and a traffic-jam ending point which arerepresented by traffic-jam information received by the trafficinformation receiver 6 is taken. Here, the travel time represented bythe traffic-jam information received by the traffic information receiver6 represents the current travel time required between the traffic-jamstarting point and the traffic-jam ending point which is actuallymeasured. A dynamic travel time required for each link is calculatedfrom the static travel time required for the link by the followingequation:

Dynamic travel time=M−(M×Y/X)+N

[0038] Here, as shown in FIG. 4, X represents the link length of a link400, M represents a static travel time calculated for the link 400, Yrepresents the length of a part 401 contained in the link 400 of asection between the traffic-jam starting point and the traffic-jamending point, and N represents a travel time of the part 401 which iscalculated on the basis of the travel time received by the trafficinformation receiver 6.

[0039] If the value of the dynamic travel time calculated by the aboveequation is larger than the static travel time by a predetermined rateor more (two times or more), it is estimated that the reception contentof the traffic information receiver 6 may contain an error, and thus thestatic travel time is directly used as the dynamic travel time.

[0040] Subsequently, for each calculation point, the sum of the dynamictravel times calculated for the respective links between the currentposition and the calculation point is calculated, and it is set as anestimated travel time required to travel from the current point to thecalculation point concerned. Further, the total link length calculatedfrom the respective links between the current point and the calculationpoint is set as a travel distance from the current point to thecalculation point (step 303).

[0041] Subsequently, the sum of the static travel time required for therespective links from the current position to the destination issubtracted from the estimated travel time calculated, and the ratio ofthe subtraction result to the estimated travel time is calculated as atraffic-jam rate (step 304).

[0042] The travel time required to travel to each calculation point isdisplayed together with the travel distance to the calculation pointconcerned as shown in FIG. 5, for example.

[0043] In FIG. 5, the estimated travel time 502 and the travel distance503 to each calculation point are displayed at both the right and leftsides of the name 501 of each of the interchanges, intersections andservices represented by the node information 31 of nodes (excluding thedestination) selected as calculation points. A road between calculationpoints is displayed as a line segment 505 connecting the names of thenodes, and the name 504 of the road is displayed on its side. A linesegment 506 approximately representing a traffic-jam section specifiedby a traffic-jam starting point and a traffic-jam ending point, theinformation of which is received by the traffic information receiver, isdisplayed with every different color on the line segment 505. A mark 510representing a regulation content represented by regulation informationreceived by the traffic information receiver 6 is displayed in theneighborhood of a regulated place. Further, the estimated travel time507 and the travel distance 509 to the destination and a bar graphshowing the traffic-jam rate are displayed at the upper side.

[0044] In the calculation of the dynamic travel time described above,the static travel time is directly used as the dynamic travel time whenthe dynamic travel time is larger than the static travel time by apredetermined rate or more. On the basis of regulation informationreceived by the traffic information receiver 6, the predetermined ratefor the dynamic travel time of a traffic-jam section containing atraffic-jam place which is estimated to be caused by a trafficregulation may be set to a value larger than that in the other cases.This is because when a traffic jam is caused by a traffic regulation,the dynamic travel time may be large irrespective of a reception errorof the traffic information receiver 6.

[0045] As described above, according to this embodiment, the estimatedtravel time is calculated in consideration of the traffic-jam andtraffic regulation information taken from the traffic informationcommunication system. Therefore, even when a traffic jam occurs ortraffic regulation is carried out, an estimated travel time conformingmore to actual traffic conditions can be calculated.

[0046] In this embodiment, the processor 1 may be a computer having aCPU, a memory and a proper OS. In this case, each process executed bythe processor 1 is implemented by the CPU executing a program in whichthe procedure of each process is described. In this case, these programsmay be supplied to the processor 1 through a storage medium such as aCD-ROM or the like.

[0047] As described above, according to the present invention, anestimated travel time conforming more to actual traffic conditions canbe calculated.

What is claimed is:
 1. A route searching apparatus for searching arecommendable route to a destination comprising: means for storing mapdata representing road maps; means for receiving traffic jam informationrepresenting traffic jam places and a travel time needed to pass througha section in which each traffic jam place is located by communication;and travel time calculating means for setting the travel timerepresented by the traffic jam information as an effective travel timefor each traffic jam section represented by the traffic jam informationthus received while setting a travel time calculated on the basis of themap data as an effective travel time for the other sections, calculatingthe sum of effective travel times for respective sections locatedbetween the current position on the searched recommendable route and adestination or a point on the recommendable route for which an estimatedtravel time is calculated, and displaying the sum of the effectivetravel times thus calculated as the travel time needed to travel fromthe current position to the destination or the point on therecommendable road for which the estimated travel time is calculated. 2.The route searching apparatus as claimed in claim 1 , wherein saidtravel time calculating means calculates the rate of the sum of thetravel times for said traffic jam sections represented by thetraffic-jam information to the sum of the effective travel times anddisplays the rate thus calculated.
 3. A required travel time calculatingmethod for calculating a travel time required to travel from a currentposition to an end point on a given route or a point on the route,comprising the steps of: storing map data representing road maps inadvance; receiving traffic-jam places and a travel time required to passthrough a section in which each of the traffic-jam places is located bycommunication; setting the travel time represented by the traffic jaminformation as an effective travel time for each traffic jam sectionrepresented by the traffic jam information thus received while setting atravel time calculated on the basis of the map data as an effectivetravel time for the other sections; and calculating the sum of effectivetravel times for respective sections located between the currentposition on the searched road and the end point or the point on theroute for which an estimated travel time is calculated, as the traveltime needed to travel from the current position to a destination or apoint on a recommendable road for which the estimated travel time iscalculated.
 4. A storage medium for storing programs which are read outand executed by a computer, characterized in that said program makessaid computer execute a step of receiving traffic-jam places and atravel time required to pass through a section in which each of thetraffic-jam places is located; a step of setting the travel timerepresented by the traffic jam information as an effective travel timefor each traffic jam section represented by the traffic jam informationthus received while setting a travel time calculated on the basis of themap data, previously stored by the computer, as an effective travel timefor the other sections; and calculating the sum of effective traveltimes for respective sections located between the current position onthe searched road and the end point or the point on the route for whichan estimated travel time is calculated, as the travel time needed totravel from the current position to a destination or a point on arecommendable road for which the estimated travel time is calculated.